The present invention relates to a method of manufacturing a semiconductor device exhibiting reduced capacitance loading. The present invention has particular applicability in manufacturing high density, multi-level semiconductor devices comprising sub-micron dimensions and exhibiting high circuit speed.
The escalating requirements for high density and performance associated with ultra large-scale integration (ULSI) semiconductor device wiring are difficult to satisfy in terms of providing sub-micron-sized, low resistance-capacitance (RC) metallization patterns. This is particularly applicable when the sub-micron-features, such as vias, contact areas, lines, trenches, and other shaped openings or recesses have high aspect ratios (depth-to-width) due to miniaturization.
Conventional semiconductor devices typically comprise a semiconductor substrate, usually of doped monocrystalline silicon (Si), and a plurality of sequentially formed inter-metal dielectric layers and electrically conductive patterns. An integrated circuit is formed therefrom containing a plurality of patterns of conductive lines separated by interwiring spacings, and a plurality of interconnect lines, such as bus lines, bit lines, word lines, and logic interconnect lines. Typically, the conductive patterns of vertically spaced metallization levels are electrically interconnected by vertically oriented conductive plugs filling via holes formed in the inter-metal dielectric layer separating the metallization levels, while other conductive plugs filling contact holes establish electrical contact with active device regions, such as a source/drain region of a transistor, formed in or on a semiconductor substrate. Conductive lines formed in trench-like openings typically extend substantially parallel to the semiconductor substrate. Semiconductor devices of such type according to current technology may comprise five or more levels of metallization to satisfy device geometry and microminiaturization requirements.
A commonly employed method for forming conductive plugs for electrically interconnecting vertically spaced metallization levels is known as xe2x80x9cdamascenexe2x80x9d -type processing. Generally, this process involves forming a via opening in the inter-metal dielectric layer or inter-layer dielectric (ILD) between vertically spaced metallization levels which is subsequently filled with metal to form a via electrically connecting the vertically spaced apart metal features. The via opening is typically formed using conventional lithographic and etching techniques. After the via opening is formed, the via is filled with a conductive material, such as tungsten (W), using conventional techniques, and the excess conductive material on the surface of the inter-metal dielectric layer is then typically removed by chemical-mechanical planarization (CMP).
A variant of the above-described process, termed xe2x80x9cdual damascenexe2x80x9d processing, involves the formation of an opening having a lower contact or via opening section which communicates with an upper trench section. The opening is then filled with a conductive material to simultaneously form a contact or via in contact with a conductive line. Excess conductive material on the surface of the inter-metal dielectric layer is then removed by CMP. An advantage of the dual damascene process is that the contact or via and the upper line are formed simultaneously.
High performance microprocessor applications require rapid speed semiconductor circuitry, and the integrated circuit speed varies inversely with the resistance and capacitance of the interconnection pattern. As integrated circuits become more complex and feature sizes and spacings become smaller, the integrated circuit speed becomes less dependent upon the transistor itself and more dependent upon the interconnection pattern. If the interconnection node is routed over a considerable distance, e.g., hundreds of microns or more, as in submicron technologies, the interconnection capacitance limits the circuit node capacitance loading and, hence, the circuit speed. As integration density increases and feature size decreases, in accordance with submicron design rules, the rejection rate due to integrated circuit speed delays significantly reduces manufacturing throughput and increases manufacturing costs.
One way to increase the circuit speed is to reduce the resistance of a conductive pattern. Conventional metallization patterns are typically formed by depositing a layer of conductive material, notably aluminum (Al) or an alloy thereof, and etching, or by damascene techniques. Al is conventionally employed because it is relatively inexpensive, exhibits low resistivity and is relatively easy to etch. However, as the size of openings for vias/contacts and trenches is scaled down to the sub-micron range, step coverage problems result from the use of Al. Poor step coverage causes high current density and enhanced electromigration. Moreover, low dielectric constant polyimide materials, when employed as inter-metal dielectric layers, cause moisture/bias reliability problems when in contact with Al, and these problems have decreased the reliability of interconnections formed between various metallization levels.
One approach to improved interconnection paths in vias involves the use of completely filled plugs of a metal, such as W. Accordingly, many current semiconductor devices utilizing VLSI (very large scale integration) technology employ Al for the metallization level and W plugs for interconnections between the different metallization levels. The use of W, however, is attendant with several disadvantages. For example, most W processes are complex and expensive. Furthermore, W has a high resistivity, which decreases circuit speed. Moreover, Joule heating may enhance electromigration of adjacent Al wiring. Still a further problem is that W plugs are susceptible to void formation, and the interface with the metallization level usually results in high contact resistance.
Another attempted solution for the Al plug interconnect problem involves depositing Al using chemical vapor deposition (CVD) or physical vapor deposition (PVD) at elevated temperatures. The use of CVD for depositing Al is expensive and hot PVD Al deposition requires very high process temperatures incompatible with manufacturing integrated circuitry.
Copper (Cu) and Cu-based alloys are particularly attractive for use in VLSI and ULSI semiconductor devices, which require multi-level metallization. Cu and Cu-based alloy metallization systems have very low resistivities, which are significantly lower than W and even lower than those of previously preferred systems utilizing Al and its alloys. Additionally, Cu has a higher resistance to electromigration. Furthermore, Cu and its alloys enjoy a considerable cost advantage over a number of other conductive materials, notably silver (Ag) and gold (Au). Also, in contrast to Al and refractory-type metals (e.g., titanium (Ti), tantalum (Ta) and W), Cu and its alloys can be readily deposited at low temperatures by well-known xe2x80x9cwetxe2x80x9d plating techniques, such as electroless and electroplating techniques, at deposition rates fully compatible with the requirements of manufacturing throughput.
Electroless plating of Cu generally involves the controlled auto-catalytic deposition of a continuous film of Cu or an alloy thereof on a catalytic surface by the interaction of at least a Cu-containing salt and a chemical reducing agent contained in a suitable solution, whereas electroplating comprises employing electrons supplied to an electrode (comprising the surface(s) to be plated) from an external source (i.e., a power supply) for reducing Cu ions in solution and depositing reduced Cu metal atoms on the plating surface(s). In either case, a nucleation/seed layer is required for catalysis and/or deposition on the types of substrates contemplated herein. A physical vapor deposition technique, such as sputtering, is useful for depositing the nucleation/seed layer.
Another technique to increase the circuit speed is to reduce the capacitance of the inter-layer dielectrics. The speed of semiconductor circuitry varies inversely with the resistance (R) and capacitance (C) of the interconnection system. The higher the value of the Rxc3x97C product, the more limiting the circuit speed. As integrated circuits become more complex and feature sizes and spacings become smaller, the integrated circuit speed becomes less dependent upon the transistor itself and more dependent upon the interconnection pattern. Thus, the performance of multi-level interconnects is dominated by interconnect at deep sub-micron regimes, e.g., less than about 0.18 micron.
The dielectric constant of materials currently employed in the manufacture of semiconductor devices for an ILD ranges from about 4.0 for dense silicon dioxide to over 8.0 for deposited silicon nitride. The value of the dielectric constant expressed herein is based upon a value of one for a vacuum. In an effort to reduce interconnect capacitance, dielectric materials with lower values of permittivity have been explored. The expression xe2x80x9clow-kxe2x80x9d material has evolved to characterize materials with a dielectric constant less than about 3.9.
One type of low-k material that has been explored is a group of flowable oxides, which are basically ceramic polymers, such as hydrogen silsesquioxane (HSQ). Such polymers and their use are disclosed in, for example, U.S. Pat. No. 4,756,977 and U.S. Pat. No. 5,981,354. HSQ-type flowable oxides have been considered for gap filling between metal lines because of their flowability and ability to fill small openings. HSQ-type flowable oxides have been found to be vulnerable to degradation during various fabrication steps, including plasma etching.
There are several organic low-k materials, typically having a dielectric constant of about 2.0 to about 3.8, which may offer promise for use as an ILD. Organic low-k materials which offer promise are carbon-containing dielectric materials such as FLARE 20(trademark) dielectric, a poly(arylene) ether, available from Allied Signal, Advanced Micromechanic Materials, Sunnyvale, Calif.; BCB (divinylsiloxane bis-benzocyclobutene), and Silk(trademark) or porous Silk(trademark) dielectric, organic polymers available from Dow Chemical Co., Midland, Mich.; and organic-doped silica glasses (OSG) (also known as carbon-doped glasses) including Black-Diamond(trademark) dielectric available from Applied Materials, Santa Clara, Calif., Aurora(trademark) dielectric available from ASM America, Inc., Phoenix, Ariz., and Coral(trademark) dielectric available from Novellus, San Jose, Calif.
In attempting to employ such carbon-containing low-k materials in interconnect technology, as for gap filling or as an ILD, it was found that their dielectric constant became undesirably elevated as a result of processing. For example, the dielectric constant of BCB was found to increase from about 2.6 to greater than about 4.
Another suitable type of low-k dielectrics are fluorine-doped silica glasses (FSG). FSG include dielectrics formed from precursor gases SiF4, SiH4, and N2O and dielectrics formed from the precursors SiF4, tetraethylorthosilicate (TEOS), and O2. Dielectrics formed from TEOS and SiF4 are known as fluorinated TEOS or FTEOS. FSGs typically exhibit a dielectric constant to about 3.6. It is believed that fluorine lowers the dielectric constant of silicon oxide films because fluorine is an electronegative atom that decreases the polarizability of the overall SiOF network.
In addition to decreasing the dielectric constant, incorporating fluorine in silica layers can also improve the gap-filling properties of the deposited films. Because fluorine is an etching species, it is believed that fluorine etches the film as it is being deposited. The simultaneous deposition/etching effect preferentially etches the comers of the gap, keeping the gap open so that it could fill small gaps with void-free FSG.
Unfortunately, there are several problems associated with some FSG layers. One problem is that poorly formed FSG layer may absorb moisture from the atmosphere, or from the reaction products associated with the deposition. The absorption of water raises the dielectric constant of the FSG. Absorbed water may also interfere with subsequent wafer processing steps. For many applications, it is desirable that FSG layers do not desorb significant water vapor below about 450xc2x0 C.
Another problem associated with some FSG layers is corrosion, if fluorine is loosely bound into the FSG lattice, or has accumulated as free fluorine on the surface, it may combine with water to form hydrofluoric acid (HF). HF may corrode, and even destroy, other device features such as metal traces or antireflective layers. One technique that is used to overcome the problems of corrosion is to form a liner over the substrate before depositing the FSG and sometimes a liner after FSG deposition. The liner is typically a thin layer of USG that acts as a barrier between device features and the FSG.
A further problem with some FSG layers are that they are unstable. In other words, the layer characteristics change over time. For example, fully formed FSG layers may form a cloudy haze, or even bubbles, within the layer when exposed to the atmosphere.
A problem associated with the use of many low-k dielectric materials is that these materials can be damaged by exposure to oxidizing or xe2x80x9cashingxe2x80x9d systems, which remove a resist mask used to form openings, such as vias and trenches, in the low-k dielectric material. This damage can cause the surface of the low-k dielectric material to become a water absorption site, if and when the damaged surface is exposed to moisture. Subsequent processing, such as annealing, can result in water vapor formation, which can interfere with subsequent filling, with a conductive material, of a via/opening or a damascene trench formed in the dielectric layer.
Capping layers provide one method of reducing reabsorption of water into low-k dielectric layers. The capping layer is typically a silicon oxide layer that is deposited onto the low-k dielectric layer with or without baking the low-k dielectric layer prior to depositing the capping layer. The capping layer may be formed in a separate deposition chamber or pump-down or the process may be streamlined to follow the low-k dielectric layer deposition in the same chamber. The capping layer protects the upper surface of the low-k dielectric from damage during removal of the resist mask and thus inhibits water absorption under many conditions. Silicon oxide capping layers, however, require an additional process step of forming the silicon oxide layer.
One problem with using silicon oxide capping layer is that the silicon oxide capping layer does not adhere well to the carbon and fluorine-doped ILD surfaces. The poor adhesion of the capping layer to the ILD increases the likelihood of diffusion or leakage of conductive materials through the porous low-k ILD, which can lead to short circuits. In addition, both carbon and fluorine-doped low-k ILD also exhibit inadequate adhesion to underlying semiconductor substrates.
Antireflective coatings (ARC) are frequently employed to help provide submicron images during photomicrographic processing. The ARC cuts down on light scattering, which helps in the definition of small images, minimizes standing wave effects, and improves image contrast during photoresist exposure. However, the use of an ARC requires additional processing steps, including spin-on and baking steps. In addition ARC layers, along with capping layers, suffer from poor adhesion to the ILD surface.
The term semiconductor devices, as used herein, is not to be limited to the specifically disclosed embodiments. Semiconductor devices, as used herein, include a wide variety of electronic devices including flip chips, flip-chip/package assemblies, transistors, capacitors, microprocessors, and random access memories, etc. In general, semiconductor devices refer to any electrical device comprising semiconductors.
There exists a need for methodology enabling the use of low-k fluorine-containing dielectric materials as an ILD in high-density, multi-level connection patterns. There exists a particular need for methodology enabling the use of such low-k materials with low-k capping and ARC layers to avoid degradation of the low-k ILD properties while providing sub-micron feature sizes with enhanced resolution.
These and other needs are met by embodiments of the present invention, which provide a method of forming a semiconductor device with a first dielectric film on a semiconductor substrate. The first dielectric film is formed by depositing a lower layer of a fluorine-doped silica glass on a semiconductor substrate. A middle layer comprising a mixture of the fluorine-doped silica glass and a gradually increasing concentration of SiC is deposited on the lower layer and an upper layer of SiC is deposited on the middle layer. SiC has a lower dielectric constant than prior art ARC layers such as SiON.
The earlier stated needs are also met by other embodiments of the instant invention that provide a semiconductor device comprising a first dielectric film formed on a semiconductor substrate. The first dielectric film comprises a lower layer comprising a fluorine-doped silica glass, a middle layer comprising a mixture of fluorine-doped silica glass and a gradually increasing concentration of SiC, and an upper layer comprising SiC.
This invention address the needs for an improved method of forming capping layers and ARC layers on low-k ILD layers for use in high-density, multi-level interconnection patterns. This invention improves adhesion of capping layers and ARC layers to low-k ILD. The present invention enables the manufacturing of high reliability, small feature sized semiconductor devices.
The foregoing and other features, aspects, and advantages of the present invention will become apparent in the following detailed description of the present invention when taken in conjunction with the accompanying drawings.